DESCRIPTION: This application is in response to the Notice Number (NOT-OD-09-058) and Notice Title: NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications. G-quadruplex DNA secondary structures have recently emerged as a new class of cancer-specific molecular targets for anticancer drugs. There is compelling in vitro and in vivo evidence of G-quadruplex structures formed in the promoter regions of genes involved in growth and proliferation as transcriptional regulators. Our parent grant proposed to define the molecular structures of the G-quadruplexes in the promoter regions of the four oncogenes, c-Myc, bcl-2, VEGF, and HIF-1a, and their drug-complex(es). While the DNA G-quadruplexes are very promising new drug targets, the evaluation of their potential as cancer therapeutic targets depends on the understanding of biologically relevant G-quadruplex structures. To that end, it appears that a number of additional important questions need to be addressed in order to fully understand the biological roles of the promoter Gquadruplexes and to evaluate their potential as cancer therapeutic targets, in particular, the specific protein interactions of the G-quadruplex structures and the consideration of the intact molecular system of the DNA secondary structures formed in gene promoters. Thus we propose in this Revision Application to study these two important expanded aspects. The proposed research in the Revision Application will focus on the c-Myc promoter as it is the most extensively studied system. In particular, the c-Myc promoter contains a highly conserved polyG/polyC NHE III1, which controls 80-90% of the c-Myc transcription. The NHE III1 has been shown to be a silencer element and the formation of a DNA G-quadruplex structure is critical for c-Myc transcriptional silencing. Furthermore, compounds that stabilize this G-quadruplex conformation have been shown to reduce c-Myc expression and are antitumorigenic. Specifically, we propose: 1) to identify the protein(s) that bind the DNA G-quadruplex formed in the c-Myc promoter;and 2) to define the structure of the Imotif as a second target in the silencer element of the c-Myc promoter. The two specific aims are important expansions of the parent grant. Protein interactions and functions will be essential to fully understand the biological function of the DNA secondary structures in gene promoters, and the identification of the G4 interactive protein(s) is the first step towards that goal. By including the I-motif formed in the C-rich strand, the revision will expand the scope of the parent grant to the complete molecular system of the silencer element in the c-Myc promoter for drug targeting. Our long-term objective is to use a structure-based approach to rationally design small molecule compounds that specifically bind DNA secondary structures and modulate gene transcription. The Revision Application will clearly accelerate the research on targeting DNA secondary structures formed in the gene promoter regions for anticancer drug development. The two specific aims are not highly inter-dependent and both have a high likelihood of being completed in the two-year period. PUBLIC HEALTH RELEVANCE: c-Myc is an important oncogene and has been validated as potential targets for cancer therapeutic intervention. It is overexpressed in a variety of tumor types and its overexpression has been associated with poor prognosis for survival. Effective modulation of c-myc expression offers promise for the cancer treatment. The proposed research represents a novel new strategy for modulating c-myc gene expression by small molecule drugs.